Refrigeration system with compressor loading means



March 7, 1967 J. R. HARNISH 3,307,359

REFRIGERATION SYSTEM WITH COMPRESSOR LQADING MEANS Filed June 29, 19 5.ZPWOEmmIF mOOQFDO mwmzwozoo mommwmmzoo m2 mm "60050 39 E J60 mozmomdsmINVENTOR= I JAMES R. HARNISH, BY W (1% 'ATTORNEY United States l atent O3,307,369 REFRIGERATION SYSTEM WITH COMPRESSOR LOADING MEANS James R.Hamish, Staunton, Va., assignor to Westinghouse Electric Corporation,Pittsburgh, Pa, a corporafion of Pennsylvania Filed June 29, 1965, Ser.No. 467,999 7 Claims. (Cl. 62209) This invention relates torefrigeration systems, and relates more particularly to refrigerationsystems used in the cooling of air for comfort. I

Thermostatic expansion valves are the most widely used refrigerationcontrols. They operate to maintain constant degrees of superheat atevaporator outlets. Evaporator coils used with such valves usually haveadditional surfaces near their outlets for superheating the suction gas.Thus, all of the refrigerant liquid supplied by such valves to suchcoils is evaporated therein.

In multi-zone, direct expansion, air conditioning systems, as well as inother systems having varying air flow over air cooling evaporator coils,at a reduced load caused by reduced air flow, refrigerant liquiddistribution through an evaporator coil is poor so that the usualthermostatic expansion valve cannot operate properly. In 100% fresh air,direct expansion systems in which the entering air temperature varieswith the outdoor ambient, at a reduced load caused by a low airtemperature, thermostatic expansion valves cannot operate properly.Another disadvantage of a thermostatic expansion valve is that when acondenser coil is cooled by outdoor air, at low outdoor ambients, thecondensing pressure is insufiicient to operate the expansion valveproperly.

This invention uses an automatic expansion valve, preferably one havingan external equalized connected at the downstream end of an evaporatorcoil so as to respond to refrigerant pressure in the refrigerant leavingthe evaporator coil. At certain load conditions, such an automaticexpansion valve can overfeed the associated evaporator coil. A suctionline accumulator is provided to receive from the evaporator theunevaporated refrigerant liquid, and has a heat exchange coil throughwhich high pressure liquid flows on its Way to the expansion valve, withheat from the high pressure liquid evaporating the excess liquid withinthe accumulator so that no liquid refrigerant is supplied through thesuction gas line into the associated compressor, the high pressureliquid being subcooled by this action.

An advantage of such an automatic expansion valve is that it can bedesigned to flood an evaporator coil under such conditions that thecondensing pressure is insufficient to properly operate a thermostaticexpansion valve.

Such an automatic expansion valve has an additional advantage when usedin 100% fresh air, double duct or multi-zone, direct expansion systemsin which the air velocity and/or temperature can vary substantially. Insuch a system, when a refrigerant compressor is turned off by a loadcontrol such as a thermostat or a refrigerant pressure control, thetemperature or the refrigerant pressure may quickly rise and cause thecompressor to be restarted, causing frequent cycling of the latter. Toprevent such cycling, it is usual to operate a compressor continuously,and to use as a load control a refrigerant pressure responsive controlwhich can unload the compressor down to a minimum load point which maybe 25% of compressor capacity. A fault of such a control is the load onthe evaporator coil may be so low that the compressor may be operatingat 10% capacity with the result that the evaporator coil may becomeiced, and

the compressor may be damaged. So-called hot gas by-pass systems havebeen used to keep the compressor artifically loaded to its minimum loadpoint, but such systems require additional, costly equipment.

In a system embodying this invention, a thermostat is used to unload acompressor down to its minimum load point. If the load decreases belowthis minimum load point, the temperature of the evaporator coildecreases, the pressure of the refrigerant leaving the evaporator coildecreases, and the automatic expansion valve opens wider to supply morerefrigerant liquid into the evaporator coil. If the load is very low, alarge amount of liquid is sup plied by the automatic expansion valve tothe evaporator, emptying the condenser coil. When the condenser coil isempty, gas flows into the heat exchange coil of the accumulator and iscondensed therein. The gas condensing in the heat exchange coil boilsoif liquid within the accumulator, keeping the compressor loaded up toits minimum load point without any additional equipment.

An object of this invention is to use an automatic expansion valve in arefrigeration system having a suction line accumulator, and having aheat exchange coil through which high pressure liquid flows to boil offrefrigerant liquid within the accumulator.

This invention will now be described with reference to the annexeddrawings, of which:

FIG. 1 is a diagrammatic view of an air conditioning system embodyingthis invention, and

FIG. 2 is an enlarged section of the automatic expansion valve of FIG.1.

Referring first to FIG. 1 of the drawings, a refrigerant compressor C,driven by an electric motor CM, is connected by discharge gas tube 10 tothe inlet end of condensor coil 11 which is cooled by outdoor air. Theoutlet end of the coil 11 is connected by tube 12 to one end of heatexchange coil 13 within suction line accumulator 14. The other end ofthe coil 13 is connected by tube 15 containing an automatic expansionvalve 16 to the inlet of evaporator coil 17. The outlet of the coil 17is connected by tube 18 to the upper portion of the interior of theaccumulator 14. Suction gas tube 20 has a U-shaped portion 21 Within theaccumulator 14, with an oil bleed hole 23 in its base, and is connectedto the suction side of the compressor C. Portions of the tubes 12 and 20are in heat exchange contact.

The automatic expansion valve 16 which will be described in detail inconnection with FIG. 2, has a diaphragm chamber 25, the inner portion ofwhich is connected by external equalizer tube 26 to the tube 18 near theoutlet of the evaporator coil 17. A fan 27 driven by .an electric motor28 blows outdoor air over the evaporator coil 17 into the conditionedspace.

The compressor C has four cylinders CL1, CL2, CL3 and CL4, havingcylinder heads H1, H2, H3 and H4 respectively. The plungers of solenoidsS2, S3 and S4 extend into the heads H2, H3 and H4 respectively, todepress the usual suction valve reeds which are not shown, for unloadingthe cylinders CLZ, CL3 and CL4 respectively. When the solenoids areenergized, they withdraw their plungers, permitting the suction valvereeds to close during the suction strokes of the respective pistons inghe respective cylinders, for loading the respective cyliners.

An outdoor thermostat T1 has a switch 31 connected to electric supplyline L2 and to one end of energizing coil 33 of compressor motor starterMS, the other end of which is connected to electric supply line L1. Thestarter MS has a switch 35 which closes when the coil 33 is energizedand connects the motor CM to the supply lines L1 and L2.

A space thermostat T2 responds to the temperature of the air within theconditioned space, and has a plunger 36 pivoted to switch blade 38between the ends of the latter. The blade 38 is pivoted at one end tofixed support 39, and is curved so as to contact in succession, switchcontacts 42, 43 and 44 on increases in temperature. The blade 38 isconnected by wire 46 to the line L2. The contact is connected by wire 4%to one end of solenoid S2. The contact 43 is connected by wire 50 to oneend of solenoid S3. The contact 44 is connected by wire 51 to one end ofsolenoid S4. The other ends of the solenoids are connected together andby wire 48 to the supply line L1.

Referring now to FIG. 2 of the drawings, the automatic expansion valve16 has a diaphragm 56 extending across the center of its diaphragmchamber 25, with the equalizer tube connected to the chamber 25 belowthe diaphragm 56. Below the chamber 25 is a valve chamber 58 having itsinlet and outlet connected to the tube 15. The chamber 58 has apartition 60 extending between its inlet and outlet, and which has avalve opening 61 in its center. A valve piston 59 is on the lower end ofa rod 57 below the opening 61. The upper end of the rod 57 is attachedto the center of the diaphragm 56. A coiled spring 62 extends betweenthe top of the diaphragm chamber 25 and the center of the top of thediaphragm 56, and biases the piston 59 towards open position.

A reduction in the pressure of the refrigerant leaving the evaporatorcoil 17, caused by a reduction of the load on the evaporator coil, orcaused by a reduction in the condensing pressure, results in a reductionin the pressure below the diaphragm 56, permitting the spring 62 to openthe valve 16 further to supply more refrigerant liquid to the evaporatorcoil.

Operation When the thermostat T1 calls for cooling, its switch 33closes, energizing the compressor motor starter MS which closes itsswitch 35, energizing the compressor motor CM. The solenoids S2, S3 andS4- would be deenergized at this time so that the compressor cylindersGL2, GL3 and GL4 are unloaded, with the compressor cylinder GL1 inoperation. If the space temperature increases above the minimum loadpoint on the thermostat T2, the switch blade 38 moves in contact withthe switch contact 42, energizing the solenoid S2 which withdraws itsplunger to load the cylinder GL2. On a further increase in spacetemperature, the switch blade 38 moves in contact with the switchcontact 43, energizing the solenoid S3 which withdraws its plunger,loading the cylinder GL3. On a further increase in space temperature,the switch blade 38 moves in contact with the switch contact 44,energizing the solenoid S4 which withdraws its plunger, loading thecylinder GL4.

The compressor C supplies discharge gas through the tube into thecondenser coil 11. Liquid from the coil 11 flows through the tube 12,the heat exchange coil 13 within the accumulator 14, the tube 15 and theautomatic expansion valve 16 into the evaporator coil 17. Gas and anyunevaporated refrigerant liquid from the coil 17 flows through the tube18 into the accumulator 14. The refrigerant liquid entering theaccumulator is evaporated by heat from the high pressure liquid flowingthrough the coil 13, the liquid flowing through the latter beingsubcooled by this action. Gas separated from the liquid within theaccumulator flows through the suction gas tube 20 to the suction side ofthe compressor C. Oil enters the bleed hole 23 and is supplied with thesuction gas to the suction side of the compressor. Any refrigerantliquid entering the oil bleed hole 23 is evaporated by heat from thehigh pressure liquid flowing through that portion of the tube 12 whichis in contact with a portion of the tube 20, the high pressure liquidbeing further subcooled by this action.

When the temperature within the conditioned space decreases to theminimum load point, the compressor cylinders GL2, GL3 and GL4 areunloaded, with the compressor G continuing in operation at its 25%capacity, minimum load point, assuming that the temperature of theoutdoor air has not decreased to the point that the thermostat T1 woulddeenergize the compressor. With the compressor continuing in operation,the temperature within the conditioned space may decrease to the pointthat corresponds to 10% compressor capacity. If this happens, theresulting decrease in the temperature of the evaporator coil 17 resultsin a corresponding decrease in the pressure of the refrigerant leavingthe evaporator coil, causing the expansion valve 16 to open wider tosupply more liquid to the evaporator coil, draining the condenser coil11. Gas then flows from the condenser coil 11 through the coil 13 withinthe accumulator 14, being conensed within the coil 13 and supplied asliquid through the valve 16 to the evaporator coil, refrigerant liquidwithin the accumulator being evaporated by this action. Thus, anartificial load of 15% capacity can be added to the 10% capacity loadunder which the compressor is operating, bringing the compressor load toits minimum 25% load point, preventing icing of the evaporator coil andpossible damage to the compressor.

At low outdoor ambients which would cause the condensing pressure todecrease below the pressure at which a thermostatic expansion valvewould operate properly, the automatic expansion valve 16 would respondto the decrease pressure at the outlet end of the evaporator coil, andwould open sufliciently to prevent the evaporator coil from becomingstarved. The valve 16 can be sized and adjusted to operate at the lowestoutdoor temperature expected to be encountered.

While a outdoor air, direct expansion, air cooling system with an aircooling evaporator coil, has been described and illustrated, thisinvention is applicable to double duct and multi-zone systems, and tosystems in which refrigeration is used to chill water which iscirculated through air cooling coils. Also, while the control responsiveto the load on the evaporator coil has been described and illustrated asa space thermostat, where water is chilled as in a shell-and-tu'be typechiller, the load control could be a thermostat responsive to thetemperature of the water flowing from the air cooling coils into thechiller.

What is claimed is:

1. A cooling system comprising a refrigerant compressor, a condenser, aheat exchange coil, and automatic expansion valve, an evaporator and anaccumulator connected in the order named in a refrigeration circuit,said coil being arranged to heat liquid within said accumulator, saidcompressor having first and second cylinders, and having means includinga solenoid for loading and unloading said second cylinder, an electriccircuit for energizing said solenoid, means for cooling a fluid withsaid evaporator, a thermostat responsive to the temperature of saidfluid, said thermostat having a switch in said circuit, an electricmotor for driving said compressor, a control switch independent of saidthermostat, and an electric circuit including said control switch forenergizing said motor.

2. A cooling system as claimed in claim 1 in which means includingresponsive to the pressure of the refrigerant flowing from saidevaporator into said accumulator is provided for adjusting saidexpansion valve towards open position on a decrease in pressure andtowards closed position on an increase in pressure.

3. A cooling system as claimed in claim 2 in which said control switchis a switch of an outdoor thermostat.

4. A cooling system as claimed in claim 1 in which said control switchis a switch of an outdoor thermostat.

5. A cooling system as claimed in claim 1 in which said evaporator is anair cooling coil, and in which said 5 thermostat is responsive to thetemperature of the air cooled by said air cooling coil.

6. A cooling system as claimed in claim 5 in which means including meansresponsive to the pressure of the refrigerant flowing from saidevaporator into said 210- 5 cumulat'or is provided for adjusting saidexpansion valve towards open position on a decrease in pressure andtowards closed position on an increase in pressure.

7. A cooling system as claimed in claim 6 .in Which References Cited bythe Examiner UNITED STATES PATENTS Wolf 62224 X McGulfey 62-503 XBergdoll 62225 X Heitchue 62-196 X Bottum 62503 X said control switch isa switch of an outdoor thermostat. 10 MEYER PERLIN, Primary Examiner.

1. A COOLING SYSTEM COMPRISING A REFRIGERANT COMPRESSOR, A CONDENSER, AHEAT EXCHANGE COIL, AND AUTOMATIC EXPANSION VALVE, AN EVAPORATOR AND ANACCUMULATOR CONNECTED IN THE ORDER NAMED IN A REFRIGERATION CIRCUIT,SAID COIL BEING ARRANGED TO HEAT LIQUID WITHIN SAID ACCUMULATOR, SAIDCOMPRESSOR HAVING FIRST AND SECOND CYLINDERS, AND HAVING MEANS INCLUDINGA SOLENOID FOR LOADING AND UNLOADING SAID SECOND CYLINDER, AN ELECTRICCIRCUIT FOR ENERGIZING SAID SOLENOID, MEANS FOR COOLING A FLUID WITHSAID EVAPORATOR, A THERMOSTAT RESPONSIVE TO